1. Field of the Invention
The present invention relates to a method of producing a thin film magnetic head for in-plane recording and reproducing or vertical recording and reproducing. More particularly, it relates to a method of producing a thin film magnetic head capable of drastically reducing a popcorn noise or a noise after write by heating a thin film magnetic circuit on a substrate at a temperature of 270.degree. C.-400.degree. C. before forming a protective layer.
2. Discussion of Background
For the thin film magnetic head, there have been known two systems, i.e. an in-plane recording and reproducing system and a vertical recording and reproducing system.
FIG. 1 is a perspective view of an important part of the thin film magnetic head for in-plane recording and reproducing disclosed in, for instance, Japanese Unexamined Patent Publication No. 84019/1980 and FIG. 2 is a cross-sectional view of the important part. In FIGS. 1 and 2, a reference numeral 1 designates a substrate, a numeral 2 designates a lower magnetic film, a numeral 3 designates a gap film made of a material such as alumina, a numeral 4 designates an upper magnetic film, a numeral 5 designates a conductive coil film, numerals 61-63 designate insulating films composed of an organic insulation resin such as novlak resin, numerals 7 and 8 designate leading parts, a numeral 9 designates an insulating film and a numeral 10 designates a protective layer.
The substrate is so constructed that an insulating film 102 such as Al.sub.2 O.sub.3 or the like is formed on a ceramic structural body 101 of a material such as Al.sub.2 O.sub.3 .multidot.TiC or the like. The thin film magnetic head is obtained by manufacturing steps wherein a number of thin magnetic head elements are formed on a single substrate and then, the substrate is cut to separate it into thin film magnetic heads. Accordingly, the substrate is generally in a form of wafer.
Each end of the magnetic films 2 and 4 constitute pole portions 21, 41 which oppose through a gap film 3 made of a material such as alumina and which serve for writing and reading.
The conductive coil film 5 constitutes a thin film magnetic circuit in association with the magnetic films 2, 4 and the gap film 3. The conductive coil film 5 has a laminated structure wherein a conductive film 5B is formed by Cu plating on an undercoat conductive film 5A which is formed by the spattering of Cu/Ti. The conductive coil film 5 is formed in a spiral form around the connect portions of the magnetic films 2 and 4 to yoke portions 22, 42.
The protective layer 10 is formed on the thin film magnetic circuit by spattering alumina so that it protects the thin film magnetic head device which is constituted by the magnetic films 2, 4, the gap film 3, the conductive coil films 5 and the interlayer insulating films 61-63. FIG. 1 shows the state of the thin film magnetic head device before the protective layer is formed.
The conventional thin film magnetic head has, however, such a disadvantage that when it is subjected to a reading operation after a write signal has been given with an interval of time of, for instance, about 10 .mu.s-20 .mu.s therebetween, a pulse-like noise which has an extremely higher peak value than that of an ordinary white noise takes place is a reading signal.
FIG. 3 shows an oscilloscope waveform in which pulse-like noises are contained in a white noise signal, wherein the abscissa has a scale indicated by a unit time of 0.5 .mu.s and the ordinate has a scale indicated by a unit voltage of 30 .mu.V. Below the waveform, there is shown a time chart of writing and reading operations with its time axis in coincidence with the time axis of the abscissa. As is clear in FIG. 3, a pulse-like noise P.sub.P having a peak value which is much higher than the level of a white noise P.sub.w is generated 1.5 .mu.s-2.5 .mu.s after a point of time t.sub.O as a standard. When a leading operation is started at t.sub.O after a writing operation has been stopped. The noise P.sub.P is called, in a field of this art, as a popcorn noise or an excess noise or a noise after write.
The mechanism of the generation of the popcorn noise P.sub.P is not entirely clear. However, it is considered that a main cause resides in a delay of forming magnetized areas at the magnetic films 2, 4 when the operation is moved from a writing operation to a stationary state. Since the magnetic films 2, 4 have magnetic anisotropy, the direction of a magnetized area which is in alignment with a direction of the axis H.sub.H of hindering magnetization (as shown in FIG. 4) at the time of the writing operation is changed to a direction of the axis H.sub.E of facilitating magnetization, which has an angular difference of 90.degree. from the direction of the axis H.sub.H of hindering magnetization (as shown in FIG. 5) at the time of the stationary state. The popcorn noise P.sub.P is likely generated due to a time lag resulted when the direction of the magnetized areas at the magnetic films 2, 4 is turned from the direction of the axis H.sub.H of hindering magnetization to the direction of the axis H.sub.E of facilitating magnetization.
Since the popcorn noise P.sub.P has its peak value V.sub.O-P and it reaches up to 100 .mu.V.sub.O-P, it is impossible to discriminate the popcorn noise from a regular reading signal, whereby an error occurs in reading operations in a magnetic disk drive. The error raises an extremely severe problem since it may reduce the utility of a thin film magnetic head. However, there has been no effective way to solve the problem. There has been proposed measures to take a long time to start a reading operation after a writing operation has been finished (post write recovery time). However, when such measures are to be adopted, it is indispensable to change a system in a magnetic disk drive apparatus, which is practically difficult. Further, the adoption of a long post write recovery time is contradictory to the demand of high density recording.